The subject invention relates to a reversible drive mechanism and, more particularly, a mechanism for driving a spindle in an up or down direction and also in a circular path about an axis parallel to the spindle. In the preferred embodiment, the device is used in a sample analysis instrument, wherein the spindle carries a pipette which is lowered into and raised from a well or like vessel holding a sample to be tested, and wherein the pipette provides a stirring action when it is lowered into the sample.
Reference is made to U.S. Pat. No. 4,224,278, entitled "An Apparatus for Performing Tests and Measurements on Liquid Samples". In that patent, an apparatus is disclosed for performing tests and measurements on various liquid samples, in particular sera. The apparatus employs three trays, each of which is provided with a plurality of storage receptacles, or wells. The first tray includes wells for samples to be tested. The second and third trays provide processing vessels, or wells. Situated above the trays are independently movable pipettes which are translatable in a horizontal plane above the trays to position the pipettes over particular wells. The pipettes are translatable in the vertical direction for adding or discharging sera sample, reagents, buffers, etc. into particular receptacles or wells. In order to accomplish this, a control must be provided for lowering the pipette just the proper distance so that it can release or take up sample, and then raise the pipette for movement to another position. At the same time, it is desirable to be able to control the pipette so that it provides a circular or stirring movement within the vessel, so as to stir the liquid contained therein. Thus, what is required is a dual purpose mechanism which provides both for the up and down movement of the pipette, and also the circular or stirring movement, with means to limit the range of vertical movement in each direction. While complicated controls of various designs can be achieved, by incorporating sophisticated electronic or electromechanical control, it is highly desirable to provide a very simple, inexpensive and reliable drive mechanism for controlling the pipette movement in the manner stated.
While the description provided will be oriented in terms of the illustrative pipette control as used in a sample analysis apparatus, it is to be understood that the invention can be adapted to any other application where a similar control is required, e.g. combined limited longitudinal movement and stirring about a longitudinal axis.